I think the all or nothing view may be the problem 'maintain spaghetti code' vs 'clean/new code'. When one inherits a code base like that one should start small. Write an automated test that tests a single scenario, add a comment that explains something particularly difficult that a developer spent a lot of time on finding out. Rename one single variable somewhere. Then gradually as one gains more knowledge start doing bigger refactors and bring more of the code under tests. It sounds like what has happened here is that a big bang rewrite was undertaken. This is almost always ill-advised.